In modern computer tomographs, the scintillators are arranged in the form of two-dimensional arrays, the flat plane of which lies perpendicular to the incident radiation. In order to ensure a high image resolution, it is necessary to prevent lateral propagation of the light signals of the individual scintillators.
They are therefore separated from one another with the aid of a reflector layer. This layer should have a high reflectivity and a low absorptivity and transmissivity for the scintillation light, in order to ensure a high luminous efficiency and low crosstalk of the light signals with neighboring scintillators. A reflector layer conventionally consists of a binder matrix to which a material in powder form with a high refractive index is added, for example TiO2, ZnO, MgO or BaSO4 particles. The particle sizes of the particles are less than 5 μm.
For the production of a detector array, gaps with a width of between 50 μm and 400 μm are left free between the individual scintillators, and these are filled with the reflector casting compound described above. So that the casting compound can readily flow into the gaps, its viscosity must not be too high. Since the powder materials increase the viscosity of a casting compound, their proportion cannot be increased to the extent necessary in order to achieve optimal optical properties. In the case of two-component epoxy resins, casting with a proportion of about 25 vol. % TiO2 powder particles is just still possible.